Cast the quota set values to integer before checking their validity

Closes-Bug: #1280159
(cherry picked from commit a444ca8646103042d665536796168252a8ca1031)

Conflicts:
	cinder/api/contrib/quotas.py

Change-Id: I56409607d435a5e2ff702ccb9f19c5d12b432570
Merge "Cast the quota set values to integer before checking their validity" into stable/havana